Does Serum Hemoglobin A1C during Early Pregnancy Predict Performance on the 1-Hour Glucose Challenge Test? [28B

Abstract

INTRODUCTION: Our objective was to determine the negative and positive predictive values of hemoglobin A1c (HgbA1c) levels, conceptualized as a screening test, in predicting abnormal 1-hour glucose challenge test (GCT) results in pregnancy. METHODS: This was a retrospective cohort study. We calculated the negative predictive value of HgbA1c levels in predicting normal 1-hour GCT (less than or equal to 140 mg/dl) and the positive predictive value in predicting an abnormal 1-hour GCT of greater than 140 mg/dl. RESULTS: We examined 635 pregnancies where the HgbA1c was measured in the same patient on the same day as or before the 1-hour GCT was performed. The median time interval between performance of the HgbA1c test and the 1-hour GCT was 95 days (IQR 56-122 days). Among women with HgbA1c levels less than or equal to 4.9, 5.0, and 5.1, the probability of their 1-hour GCT being 140 mg/dl or less was 91.3%, 91.0% and 90.1%, respectively. Among our study population, 14.5%, 22.8%, and 35.0% had HgbA1c levels less than or equal to 4.9, 5.0 and 5.1, respectively. Among women with HgbA1c levels greater than 6.1, the probability of their 1-hour GCT being greater than 140 mg/dl was 100%. However, only 0.3% of our population had HgbA1c greater than 6.1. CONCLUSION: Our study adds to the body of evidence that HgbA1c cannot replace the 1-hour GCT as a screening test for gestational diabetes, but low values can reliably predict a normal 1-hour GCT. Therefore, some women could be spared from doing the 1-hour GCT.